Cascade coater

ABSTRACT

In a cascade coater for the multiple coating of material in sheet form, the delivery gaps for the coating liquid which open onto the flow plane are each connected with a pressuredistributing chamber. This pressure-distributing chamber in turn communicates with another pressure-distributing chamber either through a narrow connecting gap or through a number of openings. The arrangement of pressure-distributing chambers one behind the other provides for an extremely uniform coating over the entire sheet width.

United States Patent Herzhoif et al. July 8, 1975 CASCADE COATER 2,76l,4l9 9/1956 Mercier [18/412 3,413,143 ll 1968 C t l. I18 4ll X [751 "erlhofl, Liverkusen; 3,442.304 51969 t alfww 1111/4 11 ux Gref, Cologne; Fml Malls, 3,469,563 9/1969 Sloan 118/325 OdemhaI-Hahnenb rg; W lfgang 3.479.989 [1/1969 Hunter et al ll8/4l0 Schweicher; Hans Frenken, both of 3,712,264 I H973 Verhoeven ll8/4Il Leverkusen; Kurt Browatzki, Opladen; Karl Voss; Willi Wasser, both of Leverkusen; Heinrich Primary Examiner-Ronald Feldbaum Bubmann, Opladen, of Germany Attorney, Agent, or Firm-Connolly and Hutz [73] Assignee: Agfa-Gevaert Aktiengesellschaft,

Leverkusen, Germany 2 'l d: l 30, 197 [2 1 c 3 57 ABSTRACT [21] Appl. No.: 384,080

In a cascade coater for the multiple coating of mate- [30] Foreign Application Priority Data n'al in sheet form, the delivery gaps for the coating liq- Aug. 3, 1912 Germany 2238133 which Open onto the flow Plane are each nected with a pressure-distributing chamber. This 52 us. Cl. 118/412 Pressure-distributing chamber in mm communicates [5]] Int. Cl? B05C 23/02 with another Pressure-distributing chamber either 58 Field of Search .1 ll8/4IO, 407, 411, 412, through a narrow connecting p or through a number 1 3 325 DIG. 4; 17 34 of openings. The arrangement of pressure-distributing chambers one behind the other provides for an ex- 56] R f r m tremely uniform coating over the entire sheet width.

UNITED STATES PATENTS 2,681,294 6/1954 Beguin 118/407 10 Claims, 4 Drawing Figures WENTEHJUL 81915 SHEET FIG. 7

FIGZ

CASCADE COATER This invention relates to a cascade coater for the multiple coating of sheet material. A coater of this kind consists of a coating block extending over the entire width of the sheet-form material with an inclined flow plane interrupted by the gaps through which the coating liquids are introduced. The coating roller, over which the sheet to be coated is guided, is arranged at a short distance from the coating block.

Cascade coaters are known in which the coating liquid initially flows through a distributing chamber situated inside the coating block and then through a narrow slot onto a downwardly inclined flow plane. The coating liquid flows downwards on this flow plane in a thin layer and successively encounters other layers formed in the same way. The various layers are superimposed without mixing to form a multilayer liquid band which flows to the lower end of the flow plane where a so-called coating meniscus is formed. This coating meniscus wets the sheet-form material over its entire width so that the sheet is uniformly coated with the multiple liquid band. Coaters of this kind are described for example in US. Pat. Nos. 2,761,417 and 2,76] ,419.

The uniformity of the coating transversely of the sheet is governed to a very large extent by the uniformity of the narrow slots which open into the flow plane. In order to obtain favorable results, these slots have to be precision made. For a slot width of 0.3 mm (cf. the above mentioned patent specifications), fluctuations in layer thickness of 3 percent occur even with a tolerance limit of only 0.003 mm. The overall irregularity produced by the machining tolerance and, additionally, by surface tension and the effect of temperature is generally much greater. In practice, therefore, it is not possible to satisfy such stringent accuracy requirements on the uniformity of the slot width over the entire width of the sheet-form material. Another disadvantage is that caked-on coating residues are extremely difficult to remove from the narrow slots. Accordingly, the coating block is generally designed in such a way that it can be opened up to make the slots accessible. However, this makes the tolerance limits even more difficult to maintain. In addition, the cleaning operation and subsequent readjustment of the coating block takes considerable time.

DOS No. 2,042,195 describes a cascade coater which has relatively wide chutes instead of narrow slots. This coater is designed for coating relatively narrow sheetform materials. At their lower ends, the chutes are provided with supply pipes. Accordingly, the coating liquid flows from the relatively narrow supply pipe into the relatively wide chute. It is impossible to prevent sedimentation in the wide chutes, in addition to which a velocity profile deviating from a completely uniform flow is inevitably developed in the chute. This velocity profile continues substantially up to the upper edge of the chute and leads to irregularities in layer thickness. It will readily be appreciated that the layer thickness is at its greatest where the rate of flow is at its maximum.

The object of the invention is to develop a cascade coater which, even with relatively wide manufacturing tolerances, still guarantees extremely high stability of the layer thickness across the sheet-form material. In addition, the new cascade coater is also intended to be suitable for coating extremely wide sheet-form materials, the uniformity of the layer thickness again having to meet extremely stringent requirements. In the context of the invention, wide sheets are sheets with a width of from I to 4 meters.

According to the invention, a cascade coater for coating sheet material, comprising a coating block extending over the entire sheet width with an inclined flow plane interrupted by a delivery gap for the or each coating liquid, and a coating roller arranged at a short distance from the coating block over which the sheet to be coated is guided, wherein the delivery gaps open into a second pressure-distributing chamber which is connected to a first pressure-distributing chamber through a narrow connecting gap or through a number of openings of small overall cross section, the cross section of the connecting gap or the overall cross section of the openings being small in relation to the cross section of the delivery gap.

The cross section of the connecting gap or the overall cross section of the openings is preferably at least 5 to ID times smaller than the cross section of a delivery gap.

The gap width s of the connecting gap is preferably amounts to between 0.3 and 0.5 mm and its length h to between 10 and 20 mm, whilst the width S of the delivery gap is between 1.5 and 5 mm and its length H between l0 and 20 mm.

According to another aspect of the invention, the first pressure-distributing chamber consists of a pipe running parallel to the coating roller which, at one end, is provided with an inlet for the coating liquid and communicates with the second pressure-distributing chamher through a number of bores. The bores are preferably arranged at intervals of l to 8 mm apart from one another and have a diameter of from 0.3 to l mm.

According to another aspect of the invention, the pipe is arranged within the second pressure-distributing chamber and is provided along its lowest generatrix with bores directed vertically downwards.

According to yet another aspect of the invention, the bores are arranged at equal intervals apart from one another, but their diameter increases from the point at which the coating liquid enters towards the end of the pipe, corresponding to the pressure drop, in such a way that the same quantity of coating liquid flows through each bore per unit of time. Alternatively, the bores can all have the same diameter, but are arranged at intervals apart from one another which decrease towards the end of the pipe, corresponding to the pressure drop, in such a way that the same quantity of coating liquid flows into the second pressure-distributing chamber per unit width. According to another alternative embodiment, the interval between and the diameters of the bores are constant. However, their diameters are sufficiently small that the flow-induced pressure drop between the point at which the coating liquid enters and the end of the pipe amounts to at most 5 percent of the total pressure prevailing in the pipe.

Finally, it has proved to be of advantage for the second pressure-distributing chamber to have a funnelshaped cross section.

The two pressure-distributing chambers are separated by a narrow flow cross section. This measure leads on the one hand to an extremely uniform velocity profile, even in cases where the delivery gaps have a relatively wide cross section. The wide delivery gaps are easy to clean. Another advantage is that the wide delivery gaps can be formed with lower relative deviations. Even with wide sheet-form materials, it is possible with the new coater to produce layer profiles with a deviation in layer thickness of less than I percent across the width of the sheet.

Embodiments of the invention are described by way of example in the following with reference to the accompanying drawings, wherein:

FIG. 1 shows a cascade coater with two pressuredistributing chambers communicating through a narrow gap.

FIG. 2 shows a modified arrangement of the pressure-distributing chambers in the cascade coater shown in FIG. 1.

FIG. 3 shows a cascade coater in which the first pressure-distributing chamber is in the form of a perforated pipe.

FIG. 4 is a cross section through the first pressuredistributing chamber shown in FIG. 3.

According to FIG. 1, the sheet I to be coated is guided over the coating roller 3 at a short distance from the coating block 2. Coating takes place at the lower end of the flow plane 4 where the coating meniscus 5 is formed. The coating liquids flow onto the flow plane 4 through the relatively wide delivery gaps 6. Inside the coating block 2, there are pressure-distributing chambers 8 and 9 separated from one another by a narrow connecting gap 7. The pressure-distributing chambers 8, 9 and the gaps 6 and 7 extend over the entire width of the sheet. The supply pipes for the coating liquids are connected to the pressure-distributing chambers 9. Accordingly, the pressure-distributing chamber 9 is referred to by definition as the first pressure-distributing chamber.

The coating liquids are delivered in quantities dosed as a function of time. Since the connecting gap 7 is extremely narrow and has a high flow resistance, a high pressure is built up in the first pressure-distributing chamber 9. It is at its greatest at the inlet point and drops by only about 5 percent towards the edges of the pressure-distributing chamber. Without the narrow connecting gap 7, i.e., without the high flow resistance between the pressure-distributing chambers, a considerably greater pressure drop would prevail over the width of the coater (up to 80 In the most unfavorable case, the flow-induced pressure drop of 5 percent towards the edges of the coater and the deviation in the plane-parallelism of the connecting gap 7 which inevitably arises out of production, result in the fact that the periodic input per unit width into the second pressuredistributing chamber 8 differs by at most 10 percent. In this way, the pressure-distributing chambers 8 are largely freed from pressureand quantity-equalizing functions. The remaining 10 percent irregularity in the throughput per unit width is fully equalized by transverse flows in the distributing chambers 8. The transverse flows are produced by the hydrostatic pressure of the column of liquid in the pressure-distributing chambers 8 and by the flow-induced pressure loss in the delivery gaps 6.

The narrow connecting gap 7 has a width s of from 0.3 to 0.5 mm and a height h offrom 10 to mm. The delivery gaps 6 have a width S of about 1.5 mm and a height H of about l5 mm. With the usual machining tolerances for the delivery gaps 6, it is possible to obtain a layer thickness uniform to i 1 percent with the dimensions specified. This represents a considerable improvement over the prior art.

The arrangement shown in FIG. 2 is similar in structure to the coater shown in FIG. I. The only difference is that the connecting gap 7 has a different location. Substantially the same results were obtained.

By contrast, FIGS. 3 and 4 show a different structure. In this case, the first pressure-distributing chamber 11 is in the form of a long tube 12 extending over the entire coating width. This pipe 12 is situated completely within the second pressure-distributing chamber 13. Instead of a narrow connecting gap, bores I4 are arranged along the lowest generatrix of the pipe (see FIG. 4). A considerable pressure gradient builds up in these bores. Only a comparatively small pressure drop prevails in the following annular gap 15 between the pipe 12 and the inner wall of the second pressuredistributing chamber 13.

Whereas, in the case of the coaters shown in FIGS. 1 and 2, the coating liquid is delivered in the middle of the first pressure-distributing chamber 9, a lateral feed 16 is provided in the arrangement shown in FIGS. 3 and 4. Accordingly, the first pressure-distributing chamber 11 is filled with the coating liquid from the side. The inevitable drop in pressure from the point 16 at which the coating liquid enters the first pressure-distributing chamber 11 to the end of the pipe 12 can be eliminated by the following alternative measures:

1. The interval A of the bores from one another is constant over the entire length of the pipe. By contrast, the diameter of the bores increases steadily from the pipe inlet to the end of the pipe. The diameter of the bores is graduated in such a way that the same quantity of coating liquid flows through each bore per unit time.

2. The diameter of the bores is constant over the entire length of the pipe. By contrast, their interval A decreases towards the end of the pipe. Accordingly, the intervals are selected in such a way that the same quantity of coating liquid flows into the second pressure-distributing chamber 13 per unit width.

3. The intervals between and the diameters of the bores are constant. However, the diameter of the bores is selected in such a way that the flowinduced pressure drop between the point 16 at which the coating liquid enters and the end of the pipe amounts to at most 5 percent of the overall pressure prevailing in the pipe.

For reasons of flow and production technology, these three measures result in a flow deviation of at most 10 percent in the second pressure-distributing chamber 13 (based on the unit width.) This remaining IO percent is then equalized again by transverse flows in the second pressure-distributing chamber I3 and in the delivery gaps 6. In this respect, the conditions are substantially the same as those prevailing in the arrangements shown in FIGS. I and 2.

The delivery gaps 6 in the arrangement shown in FIGS. 3 and 4 have a width S of from 1.5 to 2 mm and a height H of from 15 to 20 mm. The pipe I2 has a diameter of about 30 mm. The bores 14 have a diameter of from 0.3 to 1 mm, depending upon the arrangement (cf. measures 1 to 3). Accordingly, the interval A between the bores 14 is between I and 8 mm. As with the coater shown in FIGS. 1 and 2, it was possible in this case to obtain a layer thickness uniform to i l percent.

One particular advantage of this coater is the special configuration of the pressure-distributing chambers H and 13, by virtue of which deposits of solids present in the coating liquid and, hence, undesirable reductions in cross section and cleaning difficulties are avoided.

The examples quoted relate to two-layer coating. The coaters can of course also be used for one-layer coating. The following Example relates to one-layer coating with the coater shown in FIGS. 3 and 4. The dimensions of the coater and the flow data for coating a sheet of film with a photographic emulsion are quoted.

EXAMPLE 1. Dimensions of the coater Width of the delivery gap (coating width) 1 H mm Inclination of the flow plane 4 23 Width S of the delivery gap 6 1.5 mm Height H of the delivery gap 6 l7.() mm Radius of the circular part of the second pressure-distributing chamber l3 16.0 mm Outer radius of the pipe l2 12.5 mm Inner radius of the pipe 12 10.0 mm Interval between the bores 14 (constant interval A) 2.0 mm Diameter of the bores l4 (constant diameter) 0.4 mm

2. Flow data Silverhalide gelatin solution. viscosity 10 c Meterin l.l l/min Speed 0 substrate l m/min Wet layer thickness 50 um Pressure of the gelatin solution on entry into the pipe l2 X55 mWC Pressure of the gelatin solution at the end of the pipe l2 l5] mWC Pressure drop of the gelatin solution from the inlet it: into the pipe l2 to the end of the pipe 12 2.6l Pressure of the gelatin solution in the second pressure-distributing chamber l3 below the bores I4 76 mWC Pressure difference between the first and second pressure-distributing chambers approximately 77 mWC Uniformity of the profile on the flow plane 4 11.0

What we claim is:

l. A cascade coater for coating sheet material, comprising a coating block extending over the entire sheet width with an inclined flow plane interrupted by a delivery gap for the delivery or each coating liquid, and a coating roller arranged at a short distance from the coating block over which the sheet to be coated is guided, wherein the delivery gaps open into a second pressure-distributing chamber which is connected to a first pressure-distributing chamber through a narrow connecting gap means, the cross section of the connecting gap means being small in relation to the cross section of the delivery gap.

2. A coater as claimed in claim 1, wherein the cross section of the connecting gap means is at least 5 to ID times smaller than the cross section of the delivery gap.

3. A coater as claimed in claim 1, wherein the connecting gap means is a single connecting gap, the width of the connecting gap is between 0.3 and 0.5 mm and its length is between l0 and 20 mm, while the width of the delivery gap is between L5 and 5 mm and its length is between l0 and 20 mm.

4. A coater as claimed in claim 1, wherein the first pressure-distributing chamber consists of a pipe running parallel to the coating roller which, at one end, is provided with an inlet for the coating liquid and is connected to the second pressure-distributing chamber through a connecting gap means comprising a number of bores.

5. A coater as claimed in claim 4, wherein the bores are arranged at intervals of l to 8 mm from one another and have a diameter of 0.3 to l mm.

6. A coater as claimed in claim 4, wherein the pipe is arranged within the second pressure-distributing chamber and is provided along the lowest generatrix with the bores directed vertically downwards.

7. A coater as claimed in claim 4, wherein the bores are arranged at equal intervals apart, but increase in diameter from the inlet for the coating liquid to the end of the pipe in such a way that the same quantity of coating liquid flows through each bore per unit time.

8. A coater as claimed in claim 4, wherein all the bores have the same diameter, but the intervals separating them decrease towards the end of the pipe in such a way that the same quantity of coating liquid flows into the second pressure chamber per unit width.

9. A coater as claimed in claim 4, wherein the intervals between and the diameters of the bores are constant and their diameters are sufficiently small that the flow-induced drop in pressure between the inlet for the coating liquid and the end of the pipe amounts to at most 5 percent of the overall pressure prevailing in the pipe.

10. A coater as claimed in claim 1, wherein the second pressure-distributing chamber has a funnel-shaped cross section. 

1. A cascade coater for coating sheet material, comprising a coating block extending over the entire sheet width with an inclined flow plane interrupted by a delivery gap for the delivery or each coating liquid, and a coating roller arranged at a short distance from the coating block over which the sheet to be coated is guided, wherein the delivery gaps open into a second pressure-distributing chamber which is connected to a first pressure-distributing chamber through a narrow connecting gap means, the cross section of the connecting gap means being small in relation to the cross section of the delivery gap.
 2. A coater as claimed in claim 1, wherein the cross section of the connecting gap means is at least 5 to 10 times smaller than the cross section of the delivery gap.
 3. A coater as claimed in claim 1, wherein the connecting gap means is a single connecting gap, the width of the connecting gap is between 0.3 and 0.5 mm and its length is between 10 and 20 mm, while the width of the delivery gap is between 1.5 and 5 mm and its length is between 10 and 20 mm.
 4. A coater as claimed in claim 1, wherein the first pressure-distributing chamber consists of a pipe running parallel to the coating roller which, at one end, is provided with an inlet for the coating liquid and is connected to the second pressure-distributing chamber through a connecting gap means comprising a number of bores.
 5. A coater as claimed in claim 4, wherein the bores are arranged at intervals of 1 to 8 mm from one another and have a diameter of 0.3 to 1 mm.
 6. A coater as claimed in claim 4, wherein the pipe is arranged within the second pressure-distributing chamber and is provided along the lowest generatrix with the bores directed vertically downwards.
 7. A coater as claimed in claim 4, wherein the bores are arranged at equal intervals apart, but increase in diameter from the inlet for the coating liquid to the end of the pipe in such a way that the same quantity of coating liquid flows through each bore per unit time.
 8. A coater as claimed in claim 4, wherein all the bores have the same diameter, but the intervals separating them decrease towards the end of the pipe in such a way that the same quantity of coating liquid flows into the second pressure chamber per unit width.
 9. A coater as claimed in claim 4, wherein the intervaLs between and the diameters of the bores are constant and their diameters are sufficiently small that the flow-induced drop in pressure between the inlet for the coating liquid and the end of the pipe amounts to at most 5 percent of the overall pressure prevailing in the pipe.
 10. A coater as claimed in claim 1, wherein the second pressure-distributing chamber has a funnel-shaped cross section. 